The present invention relates to a system for controlling propulsion for a motor vehicle provided with:
an internal combustion engine,
a transmission including a gearbox provided with associated actuator means,
a reversible electrical machine which includes a rotor and a stator and which is interposed between the internal combustion engine and the transmission and can operate selectively as a generator and as an electric motor,
a first clutch and a second clutch which can be operated selectively in order to control the coupling of the rotor of the electrical machine with the transmission and with the internal combustion engine, respectively,
sensor means for providing electrical signals indicative of operating conditions of the vehicle, of the internal combustion engine, and of the electrical machine, and
control means arranged to control the internal combustion engine, the electrical machine, the first clutch, and the second clutch, as well as the gearbox actuator means, in accordance with predetermined methods, in dependence on the signals provided by the sensor means,
the control means being arranged, in particular, to implement a stop-start function in which, in a stop stage, upon the occurrence of first predetermined operating conditions of the vehicle, the internal combustion engine is disconnected from the electrical machine and from the transmission and is switched off and then, in a subsequent start stage, upon the occurrence of second predetermined operating conditions of the vehicle, is automatically restarted by the electrical machine, operating as a motor, and is then reconnected to the transmission.
A propulsion control system of this type is described in prior International patent application PCT/EP01/01105. This control system is characterized in that, in the start stage, the electrical machine, operating as an electric motor, is connected to the transmission, whilst a predetermined gear (preferably first gear) is engaged in the gearbox so that the vehicle is initially propelled purely by the electrical machine. In predetermined operating conditions, a change from the predetermined gear to a higher gear, preferably second gear, is then brought about and, during this gear change, the internal combustion engine is connected to the electrical machine, operating as a motor, in order to bring about starting of the internal combustion engine, and the internal combustion engine is then connected to the transmission so that, upon completion of the start stage, the vehicle is propelled by the internal combustion engine and possibly also by the electrical machine.
This known control system advantageously utilizes the advantages of stop-start operation (reduction of fuel consumption and of emissions of pollutant gases) with little impact on the driveability of the vehicle and on driving comfort.
However, the solution proposed in the above-mentioned International patent application has a limitation, which is represented by the low maximum torque which can be delivered by the electrical machine when it is operating as a motor. This limitation translates into a limitation of the possible acceleration of the motor vehicle, particularly during the start stage. If, during such a start stage, the driver demands the delivery of a high torque and hence a fast acceleration of the vehicle by fully depressing the accelerator pedal, such a demand can only be satisfied after the change from the predetermined gear to the higher gear. Clearly, this represents a disadvantage from the point of view of the driveability of the vehicle.
This disadvantage could indeed be at least partly prevented by the use of an electrical machine of larger dimensions and greater power, naturally equipped with an inverter and a storage battery of correspondingly greater power. However, the weight, size and cost of this solution are greater and in fact are unacceptable.
An aim of the present invention is therefore to provide an improved propulsion-control system which overcomes the disadvantages of systems according to the prior art outlined above, without requiring the use of a higher powered and more expensive electrical machine (and the respective accessories).